Summer 2010 preliminary outlook for North America
Summary. The summer (JJA) of 2010 is forecast to be warmer than the summer of 2009 over the eastern United States, with temperatures above the 1971-2000 average. In contrast, mean seasonal temperatures in the Pacific Northwest and western Canada are expected to be below the average. The forecast confidence is relatively high for above normal June temperatures in the Southwestern and Southeastern United States. In July the probability of negative temperature anomalies is increased for the central regions of North America. In August, the odds are in favor of positive temperature anomalies in the Great Lakes region.
Discussion
The seasonal temperature anomaly averaged over the contiguous United States is forecast to be positive in the summer (JJA) of 2010. The average temperature this summer is also expected to be higher than that in the summer of 2009. As for the spatial distribution of temperature anomalies, an anomalously warm summer is most likely for the eastern United States (Fig. 1). The magnitude of positive temperature anomalies will probably be the highest in the Southeast, where drought conditions may develop.
The previous summer was exceptionally cold in the Great Lakes region (see the review of summer 2009). There is a good chance that this summer will be much warmer; however, the magnitude of positive temperature anomalies may not be as high as in the Southeast. In contrast, a significant cooling is expected for the Pacific Northwest and western Canada.
 Fig. 2. June 2010 SAT forecast.
|
 Fig. 3. July 2010 SAT forecast.
|
 Fig. 4. August 2010 SAT forecast.
|
Monthly forecasts for June, July and August are presented in Figs. 2-4. In June (Fig. 2), the CFs for above normal temperature are the highest for the Southwest and Southeast. There is a strong positive trend in temperature fluctuations in the Southwest, although June 2009 was anomalously cold. (This forecast, however, is not simply an extrapolation of the trend, but includes many other rules.) In the Southeast, temperature does not exhibit a trend, but rather a long-term cycle with a period of about 50 years. June temperature in the past three years (2007-2009) was anomalously high, and this June will likely to continue the sequence. Colder than normal temperatures are forecast for the area from the Great Lakes eastward. This area experienced a very cold summer last year.
In July (Fig. 3), negative temperature anomalies are expected to develop over central North America. In the Southwest and Southeast, the magnitude of positive temperature anomalies will diminish, but July temperature will still be above normal in the latter region. For the western regions (Pacific Northwest and British Columbia), July will probably be the only month of the season with positive temperature anomalies.
The forecast for August (Fig. 4) has lower overall confidence, since the majority of rules for this month have not been triggered yet. It appears, however, that warmer than normal temperatures are likely for the Great Lakes region.
This forecast is different from most publicly available forecast for the summer of 2010. Thus, the CFS model and ECPC forecast indicate below normal temperatures over much of the contiguous United States and Canada. The official CPC forecast calls for enhanced chances of above-normal temperatures for the western United States. They believe that huge trends in that area are enough to overcome somewhat cool indications from the dynamical models. The CPC consolidation forecast also indicates increased chances for above normal temperatures in the southeast but they keep the probabilities modest because of cold sea surface temperatures. Below normal temperatures are forecast for the central regions of the contiguous United States, mainly due to above normal soil moisture and negative temperature trends. The forecast from the UK Met Office indicates above normal temperatures almost everywhere in North America, with probabilities 80% or greater over much of Canada and eastern United States.
